1. Technical Field
The present invention relates to a positioning method, a program, a positioning device, and an electronic apparatus.
2. Related Art
A GPS (global positioning system) is widely known as a positioning system using a satellite and is used in a positioning device built in a mobile phone, a car navigation apparatus, and the like. The GPS measures its current position by executing a positioning operation for calculating four parameter values of three-dimensional coordinate values, which indicate the position of the GPS, and a time error on the basis of information, such as the positions of a plurality of GPS satellites or a pseudo distance from each GPS satellite to the GPS.
However, in the positioning using a satellite signal transmitted from a positioning satellite, it is difficult to avoid generation of a positioning error because there are various kinds of error factors, such as multipath influence. For this reason, various techniques for reducing the positioning error have been proposed. As an example, a technique related to positioning processing using a Kalman filter is disclosed in JP-A-2001-337156.
The Kalman filter uses an estimation method based on the probability theory of estimating a state amount changing with time by using an observed value including a measurement error. In positioning processing using the Kalman filter, the current position of a positioning device is estimated, for example, by setting as an observed value a difference between an actual measurement value and a predicted value of a distance-equivalent value indicating a distance between a GPS satellite and the positioning device.
However, since it is difficult to see the measurement error included in the observed value correctly, calculation has been performed in a condition where the measurement error is set to a fixed value in the related art. In this case, however, since the measurement error largely deviates from a true value, position jump or position delay occurs in the position obtained in the positioning processing. As a result, there has been a problem that the positioning accuracy noticeably lowers.